After a decade of intense research and development, Digital Television Terrestrial Broadcasting (DTTB) has finally reached the implementation stage. DTTB services have been available in North America and Europe since November 1998. Many countries have announce their choice for a DTTB system and their implementation plan. Currently, there are three DTTB transmission standards in the world.
1) The Trellis-Coded 8-Level Vestigial Side-Band (8-VSB) modulation system developed by the Advanced Television Systems Committee (ATSC).
The ATSC was developed by the Advanced Television Systems Committee.
Grand Alliance (GA) was founded by some HDTV groups in May 1993. After the GA system was tested by Advance TV Test Center (ATTC), ATSC submitted the DTV standards to FCC in September 1995. FCC published the ATSC DTV standards on Dec. 26, 1996. The ATSC system was designed to transmit high-quality video and audio (HDTV) and ancillary data over a single 6 MHz channel. The system was developed for terrestrial broadcasting and for cable distribution. It can reliably deliver 19.4 Mbit/sec of data throughput in a 6 MHz terrestrial channel, and 38.8 Mbit/sec in a cable television channel. Its compression rate is 50:1 or higher. The ATSC system is made up of three subsystems: source code and compression subsystem, service multiplex and transport subsystem, and RF transmission subsystem.
2) The Coded Orthogonal Frequency Division Multiplexing (COFDM) modulation adopted in the Digital Video Terrestrial Broadcasting—Terrestrial (DVB-T) standard.
The DVB-T system was developed by a European consortium of public and private sector organizations, the Digital Video Broadcasting Project.
This European consortium stopped the research of analog HD-MAC system in 1993, and began to develop digital radio broadcasting. Subsequently, European ETSI published DVB-S, DVB-C and DVB-T, etc., so the DVB-T specification is part of a family of specifications also covering satellite (DVB-S) and cable (DVB-C) operations. This family allows for digital video and digital audio transport, as well as forthcoming multimedia services. The net bit rate available in an 8 MHz channel ranges between 4.98 Mbits/sec and 31.67 Mbit/sec, depending on the choice of channel coding parameters, modulation types, and guard interval duration.
For source code, DVB standards adopted an MPEG2-2 compression method and an MPEG2-1 transport stream and multiplex method. For terrestrial transmission, DVB-T specifies COFDM modulation, which is very different from ATSC 8-VSB modulation. Thus, compared with ATSC system, DVB-T can withstand high-level (up to 0 dB), long delay static and dynamic multipath distortion. The system is robust to interference from delayed signals, either echoes resulting from terrain or building reflections, or signals from distant transmitters in a single frequency network environment.
3) The Bandwidth Segmented Transmission (BST)-OFDM system for Terrestrial Integrated Service Digital Broadcasting (ISDB-T).
The ISDB-T system was developed by the Association of Radio Industries and Businesses (ARIB) in Japan. The ISDB system was developed for terrestrial (ISDB-T) and satellite (ISDB-S) broadcasting. It systematically integrates various kinds of digital contents, each of which may include multi-program video from SDTB to HDTV, Multiprogram-audio, etc. The system uses a modulation method referred to as Band Segmented Transmission (BST) OFDM, which consists of a set of common basic frequency blocks called BST-Segments. Each segment has a bandwidth of BW/14 MHz, where BW corresponds to the terrestrial television channel spacing (6, 7, or 8 MHz, depending on the region). In addition to the properties of OFDM, the BST-OFDM provides hierarchical transmission features by using different carrier modulation schemes and coding rates of the inner code on different BST-segments.
Because there are more than one DTTB system, many countries and administrations are now engaged in the process of selecting a DTTB system. Each country has specific characteristics and needs. The selection of a DTTB system must be based upon how well each modulation system meets specific conditions such as spectrum resource, policy, coverage requirements, transmission network structure, reception conditions, type of service required, objectives for program exchange, cost to the consumers and broadcasters, etc.
Based on problem analysis of these three terrestrial digital TV broadcasting systems, we have invented an original terrestrial digital TV system which meets DTV needs.